Hopper-type railroad cars are used to transport lading which is discharged through outlet gate assemblies mounted at the bottoms of the cars. Bulk lading transported by hopper cars include finely divided materials such as sugar, flour, wheat, potash and cement. The filled hopper cars are delivered to shipper's terminals for unloading.
Conventional methods used to unload hopper cars include gravity discharge, vacuum discharge and pneumatic discharge of lading. During gravity discharge lading falls by gravity through a discharge opening in an outlet gate assembly. During vacuum discharge lading falls down from the car through an outlet gate and into a closed discharge chute. A vacuum hose is connected to the discharge chute and vacuum is applied to the hose. Air drawn into the discharge chute carries the lading along the discharge chute and into the vacuum hose. During pneumatic discharge of lading a pneumatic sled is attached to the bottom of the discharge opening. The pneumatic sled includes screw-type conveyors for discharging lading from the hopper car. Compressed air is blown into the discharge opening to pressurize the inside of the hopper car and separate compacted lading. The lading falls through the discharge opening and into the screw conveyors for removal.
Each unloading method requires its own specialized equipment to unload a hopper car. Nonetheless, a shipper may require one unloading method over another. Typically, a shipper's terminal can accommodate only one method for unloading a hopper car. For instance, one shipper may gravity discharge sugar from a hopper car while another shipper may vacuum discharge sugar from a hopper car. As a result, shipper requirements dictate the type of hopper car used to transport lading to discharge terminals.
To provide flexibility to the railroads, conventional outlet gate assemblies permit gravity discharge, vacuum discharge or pneumatic discharge. The same hopper car can accommodate all shippers without regard to the particular discharge method required. This flexibility gives the railroads increased freedom in scheduling hopper cars, particularly for seasonal loads, and reduces operating costs.
The known multi-discharge gate assemblies include a rectangular frame that defines a rectangular discharge opening at the bottom of the assembly. A pair of opposed vacuum nozzles are mounted on the frame and open into the discharge opening. Upper and lower gates are mounted in the frame. Each gate is supported on its edges by the frame and extends through a slot in one side of the frame. Slot seals prevent exposure of lading to outside contaminants. The gates are movable between closed and opened positions to open and close the upper and lower ends of the assembly.
An opening and closing drive shifts the upper gate between open and closed positions. Fixed racks are mounted on frame extensions located outside sized to extend through a slot and beyond the discharge opening to the frame extension. A walking operating shaft is mounted on the end of the upper gate outside the discharge opening and carries pinions which engage the racks. The operating shaft is rotated in an appropriate direction to move the upper gate and the operating shaft in a desired direction.
A locking mechanism allows the upper gate to be locked to the lower gate so that both gates move together. When the gates are locked together, rotation of the operating shaft simultaneously moves both the upper and lower gates between opened and closed positions. When the gates are unlocked from one another, rotation of the operating shaft moves the upper gate only and the lower gate is stationary.
During gravity or pneumatic sled discharge of lading, the door locking mechanism locks the upper and lower gates together. The operating shaft is rotated to move the upper and lower gates simultaneously from the closed position to the open position. Lading falls down through the gate assembly.
During vacuum discharge of the hopper car, vacuum hoses are attached to the vacuum nozzles. The door locking mechanism is unlocked. The operating shaft is rotated to open the upper gate only. The lower gate remains closed. Lading falls down into the frame but cannot exit through the bottom of the assembly. Vacuum draws air and lading into the vacuum hoses.
The conventional gate assembly includes a bulky rack and pinion drive located to one side of the opening. The pinion gears travel over fixed racks as the upper gate moves between opened and closed positions. The stationary racks extend away from the discharge chute a distance equal to the travel of the upper gate. This type rack and pinion drive greatly increases the size, cost and complexity of the outlet gate assembly.
Thus, there is a need for an improved multi discharge outlet gate assembly having a simpler, more compact and less expensive gate drive.